Symmetry reduction by surface scattering and mobility model for stressed 〈100〉/(001) MOSFETs

It is demonstrated that the gate interface breaks the equivalence between vertical and transverse direction for the mobility in 〈100〉/(001) pMOSFETs, leading to 6 instead of 3 independent 1st order piezoconductance coefficients. This is found from Monte Carlo (MC) simulations yielding different effective mobilities for uniaxial vertical and transverse stress, which can be explained in terms of energy and parallel-momentum conservation upon specular surface scattering. A mobility model with stress-dependent 1st order piezoconductance coefficients is presented. This model is shown to reproduce well corresponding MC effective mobilities not only for low, but also for high stress.